The DXT2222A-13 is a possible choice for pre-driver as the power is fairly low. For the driver
the board layout to get the tab on enough copper is nasty space wise. I've used that part
and its otherwise a good SOT89 2N2222A maybe a tiny bit better (lead inductance is smaller).
It would be hard to apply to the current V3 and V4 board.
The SMT 5109 is not useful for the same reasons [board layout] for the driver. it
would work a bit better for the pre-driver.
NOTE on SOT89 the pinout is BCE and the boards are EBC so attaching them to existing
boards would be very messy with lots of cutting and jumpers even for test reasons. They
would also need a flag to radiate the heat (copper .020 thick by .25 side and .4 tall.).
Someone else can do that for a test.
The BFR106 works for Q90 and also in the 45mhz IF amp section very well. Its not a choice
for other parts of the radio. As more power capability is needed or 3904 is fine.
One possible layout I looked at was strip the power amp completely Q90 though IRF510s
and have a board above the main board carry the input filters, improved amp, then
using the output filters on the lower main board. Two pieces of coax and a few control
lines. That and other added features as there would be space. That would make an
upgrade far easier as its a whole board and wires.